Method of manufacturing and installing insulated staves for tank lining



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ljnired States Patent METHGD OF MANUFACTURING AND INSTALL- ING INSULATED STAVES FOR TANK LINING Willard L. Morrison, Lake Forest, Ill., assignor to Union Stock Yards and Transit Company of Chicago, Chi- My invention relates to the manufacture and installation of insulating lining for metal tanks adapted to contain liquified hydrocarbons and the like at atmospheric pressure and at temperature far below the freezing point of water.

The tanks which I wish to line are gas tight metal tanks having the usual openings preferably at the. top for filling and emptying. The lining I propose to use to insulate the tank is preferably of balsa wood or the like. However, any type of fibrous or porous self-supporting insulating lining may be used provided it is such a lining material as will not deteriorate from direct contact with the cold liquid and will protect the metal tank wall from direct contact with the liquid which might reduce the temperature of the wall to a dangerously low point.

I propose to assemble the balsa wood or other insulating material into a plurality of staves which can be assembled inside the tank to provide a continuous unbroken insulating wall between the cold liquid and the metal tank wall.

Balsa wood of commerce usually reaches the market in this country in comparatively small pieces, a few feet in length and but a few inches in width and thickness. The small balsa wood sticks will be assembled or built up into a plurality of large self-supporting staves or beams, the separate smaller pieces being assembled, glued together and cut to proper dimensions to line the tank.

In order that the tank lining installed at room temperature, may be pre-stressed or pre-compressed in the steel tank, so as to insure that when the lining is contacted and shrunk by the very cold contents of the tank, the lining will still be continuous, some means must be provided to erect the lining in such pre-compressed condition that when it is'chilled .by the contents and shrunk the lining will remain continuous without voids or gaps and will prevent any contact between the steel tank wall and the extremely cold liquid contained therein.

A good way to accomplish this is to so dry the balsa wood and the staves before assembly in the tank that when the lining resumes its natural moisture content the resultant expansion will be greater than the contraction caused by cold liquid when the tank is filled.

I propose therefore to dry all of the elements of each stave down to a point far below the moisture content of the wood when exposed to air of normal humidity. The dried pieces will be removed from the drying chamber, cut to proper dimensions, assembled and cemented in a stave and the staves will be assembled in the tank in such a length of time that the wood will not be able to absorb enough moisture from the air to expand it appreciably until the lining is completed and installed.

The treatment that I propose will of course be carried out by usual wood working apparatus and the work flow starting with the separate wood sections from the drying room to final installation in the tank is as follows.

The process of the persent invention may be described most conveniently by having reference to the several steps 2,770,272 Patented Nov. 13, 1956 which are performed sequentially. In the annxed drawing such steps are illustrated as being performed at different stations through which the work progresses. It should be understood, of course, that certain of these stations or steps may be performed at: or occur in the same physical location.

Station N0. 1 is the drying room where the separate pieces of balsa wood are dried and stored. Each piece of wood is separately withdrawn from the drying room and taken to station No. 2 where by any suitable planer one board face of each balsa wood piece no matter what its size will be planed smooth and true.

Each piece of wood is then taken to tation No. 3 where the two ends are sawed off simultaneously in planes perpendicular to the initial plane face and also perpendicular to the longitudinal axis thereof, then the opposite face is planed parallel to the first face .at station 4. Each planed piece is then provided with glue on each of the opposed parallel planed surfaces at glue application station :No. 5. Usually the width of the individual pieces are substantially uniform. In case a piece has excess Width one edge will be planed enough so that piece will conform to the other pieces. This may be done, after the faces are planed, at station No. 4a.

Assuming that the width of all the pieces with glue on the planed faces are substantially uniform a plank is then assembled, the glued pieces being brought together in sufiicient numbers so that a plank is formed, the width of which, built up from a suitable number of the pieces, is approximately the thickness of the desired insulation. The ends of the pieces will usually not be planed but left smoothly sawed and glue may or may not be, applied to the abutting sawed ends. The lengths of the pieces will be so selected and they will be so arranged that the joints are always broken. This takes place at station No. 6. The plank thus formed will be constantly built up at one end and will be cut off at the other end. Sections of the assembled plank are, step by step, subjected before being cut off, to pressure, laterally and transversely, the glue being subjected thereby to substantial pressure. This pressure is maintained until the glue is cured by the dielectric heat of eddy currents set up between electrode perpendicular to the glue plane at station No. 7, this being merely an application of usual dielectric heating.

As the plank passes from the glue curing station 7 and extends in proper length the plank is cut off not perpendicular to the axis of the plank but at an angle of approximately 45 degrees, first inclined one direction and then inclined in the other so that each plank is trapezoidal in shape in the plane of the width of the plank. This is done at station No. 8. Thereafter each plank is sent through a moulder at station No. 9, both faces and edges being simultaneously planed to proper final dimensions. This results in the production of an individual stave or beam.

Each stave is then contoured on its outer edge to conform to the contour of the tank. Steel tanks of the size here in question preferably welded are never exactly cylindrical and the curvature and position of the plates are never exactly correct so by any suitable means the outer edge of each stave is cut or shaped to fit the inner periphcry of the wall of the tank at the point where it is to be applied so that there will be contact of the stave and tank wall throughout its entire length. This takes place at station No. it), which may be inside or outside of the tank.

A glue layer will be formed between one face of the stave and the adjacent previously installed stave and if desired between the shaped edge of the stave and the tank wall at station No. 11 and pressure is there applied by any suitable means to force the new stave into contact with and compress the glue between it and the preceding stave. While such pressure is being applied the glue is cured dielectrically, the wall of the tank acting as one electrode in opposition to an electrode engaging the inner face of each stave.

This build up is continuous, staves being formed and installed until the tank is completely lined.

The method of manufacturing the beams for the top and bottom is the same as for the staves for the side except that the top and bottom staves are of different lengths conforming to their position as they extend across the top and bottom of the tank, and the beams are par- .allel sided whereas the staves have their opposed sides inclined to conform to the radius of the cylindrical tank.

Both vertical staves and the roof and floor beams are as above indicated cut on the bias at their ends because this provides a 45 degree joint or contact between the top and sides and the bottom and sides of the insulating lining which makes possible a tight fitting bond between the ends of staves and beams at all times.

The balsa wood when dried before it starts along the How path will usually be brought down to less than 5 percent moisture which causes sufiicient shrinking so that when it is allowed to later absorb moisture, say to percent, to expand back to normal size the tank wall will be under tension and the lining under compression which compression will be reduced when the cold fluid enters the tank but will still be great enough to keep the insulating lining tight.

Usually it will not be necessary to again dry the wood as it passes from the initial drying room through the various work stations to final installation in the tank. However, if desired the wood may be again dried at any stage in the operation.

After the tank is completely lined with the dry wood staves and beams moisture will be introduced in the form of moist air, or steam or if ample time is available in the form of the usually moist ambient air. moisture penetrates the porous wood and expands it back to normal thus insuring the prestressing or compressing of the wood necessary to more than compensate for the shrinking which will later result from the cooling of the lining by contact with the cold liquid in the tank.

I claim:

1. The method of providing an insulating lining tor a cylindrical metal tank which consists in shrinking a plurality of pieces of lumber, cutting, fitting, assembling and gluing said shrunk pieces to form separate interfitting staves and beams, assembling the beams in the tank to form a floor, assembling the staves within the tank above the floor to form a lining for the cylindrical tank wall, assembling beams above the staves forming a roof lining, cementing adjacent staves and beams together as the insulating lining is built up, and then causing the wood This forming the assembled staves and beams to expand to exert a tension on the tank walls with resultant compression of the wood lining.

2. The method of lining and insulating a metal tank which consists in first extracting moisture from a plurality of pieces of lumber whereby substantial shrinkage occurs, cutting, fitting, assembling and gluing the dried wood pieces to form staves and beams of pre-determined size and shape,.assembling said staves and beams in the tank to form an insulating lining therefor, cementing adjacent staves and beams together as the insulating lining is built up, then. causing the wood to absorb moisture until it has retured to its normal moisture content and expanded to exert a tension on the tank walls with resultant compression of the liner.

3. The method of providing an insulating lining for a cylindrical metal tank which consists in shrinking a plurality of pieces of lumber, cutting, fitting, assembling and gluing said shrunk pieces to form separate interfitting staves and beams, assembling the beams in the tank to form a floor, assembling the staves within the tank above the floor to form a lining for the cylindrical wall, assernbling beams above the staves to form a roof lining, cementing adjacent staves and beams together as the insulating lining is built up, the cementing of the beams and staves together including the step of first coating opposed surfaces with a heat sensitive adhesive then subjecting such adhesive to dielectric heat with the wall of the tank serving as one of the electrodes.

4. The method of lining and insulating a metal tank which consists in first extracting moisture from a plurality of pieces of lumber whereby substantial shrinkage occurs, cutting, fitting, assembling and gluing the dried wood pieces to form staves and beams of pre-determined size and shape, assembling said staves and beams in the tank to form an insulating lining therefor, cementing adjacent staves and beams together as the insulating lining is built up, the cementing of the beams and staves together including the step of first coating opposed surfaces with a heat sensitive adhesive then subjecting such adhesive to dielectric heat with the wall of the tank serving as one of the electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,133,299 Lundin Mar. 30, 1915 1,237,533 McArthur Aug. 21, 1917 1,486,113 Baxter et al. Mar. 4, 1924 2,279,820 Hamilton Apr. 14, 1942 2,300,720 Goss Nov. 3, 1942 2,303,745 Karreman Dec. 1, 1942 2,315,742 Shipman Apr. 6, 1943 tap- 4 

